Haloalkanes and Haloarenes Test - 10

CH₃NH₂ can act as nucleophile to cause substitution reaction. (CH₃)₄N⁺ this is formed when 3 moles of CH₃NH₂ reacts with methyl halide.

The hydroxyl group of an alcohol is replaced by halogen on reaction with concentrated halogen acids, phosphorus halides or thionyl chloride. Thionyl chloride (SOCl₂) is preferred because the other two products SO₂ and HCl are escapable gases. Hence the reaction gives pure alkyl halides.

ROH + SOCl₂ → RCl + SO₂(g) + HCl(g)

CH₃CH₂Br + KCN → CH₃CH₂CN + KBr

Chlorine containing antibiotic, chloramphenicol, produced by soil microorganisms is very effective for the treatment of typhoid fever. Chloramphenicol is antityphoid drug.

Chloroquine is a synthetic halogen compound. It is used for the treatment of malaria.

As we move down the group 17, the size of atom increases as F<Cl<Br<I. Thus the bond strength of hydrogen halides reduces as HF>HCl>HBr>HI. So it is easiest to break H-I bond. Hence the decreasing order of reactivity for conversion of ROH to RX is HI>HBr>HCl>HF.

Alkyl halides react with sodium in dry ether to give hydrocarbons containing double the number of carbon atoms present in the halide. This reaction is known as Wurtz reaction.

2RX + 2Na → R − R + 2NaX

So C₆H₅CH₂CH₃ is not prepared by Wurtz reaction.

2CH₃Br + 2Na → CH₃CH₃ + 2NaBr

Vinylic halides are the compounds in which the halogen atom is bonded to an sp²-hybridised carbon atom of a carbon-carbon double bond (C = C). For example CH₂=CHBr.

The para-isomers of dihalobenzenes are high melting as compared to their ortho- and meta-isomers. It is due to symmetry of para-isomers that fits in crystal lattice better as compared to ortho- and meta-isomers. These compounds have lower solubility in water but higher solubility in organic solvents.